This research is directed toward the development of a methodology and associated model that can be utilized in planning and monitoring the prehospital phase of an Emergency Medical Services (EMS) system. Emphasis will be placed on determining policies for prehospital training (number and level) and skill maintenance in accordance with local and/or regional characteristics. This model will specify the training, continuing education and medical command options which maximize prehospital effectiveness subject to considerations of demand, community commitment, type of response desired and cost. The model is characterized by components for which very little definitive information exists. The major part of this research will respond to such questions. Randomized experiments have been designed to analyze the effect of skill maintenance and medical command on the EMS system. Descriptive analyses will be used to analyze demand, community commitment, type of response (single/dual tier, paid/volunteer, etc.), and cost. The prehospital care data system in Western Pennsylvania and the computerized algorithm performance measure developed in previous work will be major resources in effectively carrying out this project.